net: wrap sk->sk_backlog_rcv()

Wrap calling sk->sk_backlog_rcv() in a function. This will allow extending the
generic sk_backlog_rcv behaviour.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/net/tcp.h b/include/net/tcp.h
index f6cc341..438014d 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -896,7 +896,7 @@
 			BUG_ON(sock_owned_by_user(sk));
 
 			while ((skb1 = __skb_dequeue(&tp->ucopy.prequeue)) != NULL) {
-				sk->sk_backlog_rcv(sk, skb1);
+				sk_backlog_rcv(sk, skb1);
 				NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPPREQUEUEDROPPED);
 			}